The syntheses of 2,3‐dimethylidene‐ and 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptanes substituted in position C(1) are reported. The 1‐dimethoxymethyl group in derivatives2and6controls the regioselectivity of theLewis‐acid‐catalyzedDiels‐Alderadditions with methyl vinyl ketone and butynone. For the EtAlCl2‐catalyzed addition of methyl vinyl ketone to6, the regioselectivity can be reversed by a small solvent modification. The tetraene2is a versatile reagent for regioselective ‘tandem’ cycloadditions.
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METRAL et al. (1986) studied this question.
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